Tetrafluoroethylene products and methods



United States Patent 3,409,584 TETRAFLUOROETHYLENE PRODUCTS AND METHODS Francis X. Buschman, Philadelphia, and Joseph A. Dillon and John E. Sloat, Monocacy Station, Pa., assignors to L. Frank Markel & Sons, Inc., Norristown, Pa., a corporation of Pennsylvania No Drawing. Filed Feb. 3, 1966, Ser. No. 524,832 9 Claims. (Cl. 260-41) ABSTRACT OF THE DISCLOSURE A composition of matter is disclosed having both abrasion-resistant and anti-friction properties. The composition consists of a mixture of 9095% by weight of a polymer of tetrafluoroethylene and 10% by weight of zirconium silicate. The 90-95% by weight of tetrafluoroethylene polymer is comprised of approximately equal parts of virgin tetrafluoroethylene powder and powder obtained from reclaimed tetrafluoroethylene. A principal use of the new composition is in the production of tubing for accelerator cables in which a stranded steel rope is moved back and forth within the tubing.

This invention relates to a new tetrafluoroethylene composition which has substantially improved resistance to abrasive wear. The new composition also has high resistance to cold flow.

While the new composition has other uses, a principal use is in the production of tubing for accelerator cables for automobiles and trucks, throttle cables for outboard motors, and the like. Such cables usually consist of an inner stranded steel rope which, in use, is moved back and forth by the operator to control the speed of the motor of the automobile or other vechile. The stranded steel rope is contained inside a plastic tubing, the tubing is, in most cases, covered by a flat armor tape, and the armor covered tubing is ordinarily placed in an aluminum (or other metal) supporting conduit.

It has been customary to make the plastic tubing of the accelerator cable of Teflon because of its excellent anti-friction properties. Teflon, which is the trademark and well known product of E. I. du Pont de Nemours and Company, is a synthetic resin based on tetrafluoroethylene polymers.

The stranded steel rope of an accelerator cable is, over a period of time, moved back and forth a tremendous number of times within the Teflon tubing, and this back and forth movement subjects the Teflon tubing to abrasive wear.

Efforts have heretofore been made to increase the resistance of the Teflon tubing to abrasive wear, thereby to increase the life of the tubing. It has been discovered heretofore that the wear life of the tubing can be appreciably increased by mixing with the virgin Teflon powder equal parts of reclaimed Teflon powder, i.e., powder produced from reclaimed extruded or molded Teflon. Tubing extruded from such a mixture has been found to have almost twice the wear life of tubing extruded from wholly virgin Teflon powder.

A principal object of the present invention is to provide a new composition suitable for extrusion into tubing and other forms, and having substantially increased resistance to abrasive wear, as compared with compositions heretofore available.

A more specific object is to provide an extruded tubing suitable for use in accelerator cables and having substantially increased life resulting from its increased resistance to abrasive wear, as compared with heretofore available tubings.

The above objects are achieved by adding to and mixing 3,409,584 Patented Nov. 5, 1968 with the Teflon extrusion powder a minor percentage of zirconium silicate powder (ZnSiO In a preferred composition, 5 parts (by weight) of zirconium silicate powder are mixed with 45 parts of reclaimed Teflon powder and 50 parts of virgin Teflon powder. The improvement achieved in wear resistance by the addition of zirconium silicate powder is surprising indeed.

For example, Teflon tubing, used in an accelerator cable consrtucted generally as aforesaid, and extruded from a mixture of equal parts of virgin Teflon powder and reclaimed Teflon powder, did not fail, under test, until about 25,000 reciprocating strokes (cycles) of the stranded steel rope. However, when five parts of zirconium silicate were added to the blend, the extruded tubing did not fail after two million reciprocating strokes of the stranded steel rope.

Prior to the discovery that the addition of a minor percentage of zirconium silicate powder to the mix of virgin and reclaimed Teflon powders accomplishes such a surprising improvement in abrasive wear resistance, a number of other additives had been tried, but none proved satisfactory. Included among those tried, but found not satisfactory, were the following: flake glass, tin powder, tin flake; bronze flake; bronze powder; steel powder, stainless steel powder; molybdenum disulphide; and others.

The process of producing the improved tubing, using a preferred method and composition, comprises the steps of: Adding five parts of zircon (zirconium silicate) filler powder of fine particle size (200 to 400 mesh) to and tumbling it with a blend of substantially equal parts of virgin Teflon powder and reclaimed Teflon powder. The mixing and tumbling is done at a temperature of less than 72 F. The reclaimed Teflon powder is obtained from previously processed Teflon. The Teflon powders are fluffy, like flour; they are not granular. A volatile oil or lubricant, preferably naphtha, 16-21% by weight, is added to the mix before extruding. This is an extrusion aid which is subsequently removed. The mix is then extruded at pressures of the order of 10,00012,000 p.s.i., at ambient temperature, but above 72 F. The extrusion process compresses the mix into a cylindrical preform. The powders cold flow; there is no melting. After extrusion, the preform passes through an oven, at about 900 F., to fuse or sinter the compressed powders into a homogenous product, and to volatilize the naphtha lubricant. The process is a continuous one. The resulting product is found to have greatly improved resistance to abrasive wear. The product also has good resistance to cold flow. Moreover, these characteristics are obtained without any significant adverse effect on the desired electrical insulating properties of the tubing.

The following examples of tests made will illustrate the improvement in resistance to abrasive wear achieved by the addition of a minor percentage of zircon powder to the blend. In each of the following tests, steel rope was contained in, and moved back and forth in the plastic parts virgin Teflon "{5 parts zirconium silicate powder" to 50 parts virgin Teflon powder.

4- 45 parts reclaimed Teflon powder N 0 failure at 2,000,000.

5 parts zirconium silicate powder It is believed that the new mix or blend may also be extruded or molded in forms suitable for use as bearings and that such bearings will exhibit very favorable wear and cold flow properties.

While the addition of five parts (by weight) of zircon powder has been found to be optimum, it will be appreciated that some departure may be made from this percentage without going outside of the invention described and claimed.

What is claimed is:

1. A composition of matter having high abrasion resistance and a low co-efiicient of friction and consisting, at the surface as well as internally, of a mixture of 90- 95% by weight of a polymer of tetrafluoroethylene and 5-10% by weight of zirconium silicate.

2. A composition according to claim 1 characterized in that said 90-95% of tetrafluoroethylene is comprised of approximately equal parts of virgin tetrafluoroethylene powder and of powder obtained from reclaimed tetrafluoroethylene.

3. A composition according to claim 2 characterized in that said composition consists of five parts by weight of zirconium silicate powder, forty-five parts of powder of reclaimed tetrafluoroethylene and fifty parts of virgin tetrafluoroethylene powder.

4. The process of forming an abrasion resistant product comprising the steps of mixing a minor percent. e by weight of zirconium silicate powder with a major percentage by weight of tetrafiuoroethylene powder, extruding the mixture, and subjecting the extrudheat to fuse the extruded material into a homogeneous product.

5. The process of forming an abrasion resistant product material to comprising the steps of mixing approximately equal per- 3 centages by weight of virgin tetrafiuoroethylene powder with powder obtained by pulverizing reclaimed tetrafluoro- 4 ethylene, adding to said mixture and blending therewith a minor percentage by weight of zirconium silicate powder, extruding the blend, and passing the extruded material through an oven to fuse the material into a homogeneous product.

6. The processclaimed in claim 5 characterized in that the minor percentage by weight of zirconium silicate powder is of the order of 10%.

7. The process claimed in claim 5 characterized in that the minor percentage by weight of zirconium silicate powder is of the order of 5%.

8. The process claimed in claim 7 characterized in that a volatile lubricant is added to the blend before extrusion, and in that the lubricant is volatilized off in the oven.

9. The process as claimed in claim 8 characterized in that the powders are mixed at temperatures below 72 F., further characterized in that the mixture is extruded at ambient temperatures above 72 F., and in that the oven temperature is of the order of 6501500 F.

References Cited UNITED STATES PATENTS MORRIS LIEBMAN, Primary Examiner.

J. FROME, Examiner. S. L. FOX, Assistant Examiner. 

